1. Field of the Invention
The present invention relates to a cryogenic refrigerator that drives a displacer using a motor.
2. Description of the Related Art
Gifford-McMahon (GM) refrigerators are known as cryogenic refrigerators that can produce cryogenic temperatures. A GM refrigerator produces a refrigeration effect using the Gifford-McMahon refrigeration cycle, which involves reciprocating a displacer within a cylinder using a drive mechanism to create a volume change in a space within the cylinder.
A high-pressure working gas that is generated at a compressor is supplied to the displacer at a predetermined timing using a valve mechanism. Also, a regenerator material is arranged inside the displacer in order to improve cooling efficiency.
Various types of drive mechanisms are known for driving the displacer. In one known example, a motor is used as a drive source, a scotch yoke that is arranged within a housing is used to convert a rotation of the motor into a reciprocating motion, and a drive shaft that interconnects the scotch yoke and the displacer is used to drive the displacer to reciprocate.
Also, a technique is known for reducing a torque applied to the motor of such a GM refrigerator by providing a space at a front end portion of the drive shaft within the housing (referred to as “assist space” hereinafter) and adjusting the pressure within the assist space.